I'm actually hoping for something similar to what was done with Virtua Fighter 4, DragonBall Z Budokai 3, Devil May Cry 3, and probably some others: the Greatest Hits release is actually a full-blown Special Edition of the game.
Square-Enix hasn't done anything like that before, but I think it'd be opportunity to push a lot of copies out, as it'd both the players who never played KH2, and those who have, and want the bonus stuff.
So, yeah, Final Mix in the US as KH2: Special Edition, for $20. I can dream.